The role of ion drift in the formation of ionisation troughs in the mid- and high-latitude ionosphere—a review

Using results of the in situ measurements made by the DE 2 satellite, the nature of plasma structuring at high latitudes, caused by the gradient drift instability process, is described. Using noon-midnight and dawn-dusk orbits of the DE 2 satellite, it was possible to examine the simultaneous density and electric field spectra of convecting large-scale plasma density enhancements in the polar cap known as 'patches', in directions parallel and perpendicular to their antisunward convection. The results provide evidence for the existence of at least two generic classes of instabilities operating in the high-latitude ionosphere: one driven by large-scale density gradients in a homogeneous convection field with respect to the neutrals, and the other driven by the structured convection field itself in an ambient ionosphere where density fluctuations are ubiquitous.

Plasma structuring by the gradient drift instability at high latitudes and comparison with velocity shear driven processes

[1] High-rate sampling data of Global Navigation Satellite Systems ionospheric scintillation acquired by a network of GPS Ionospheric Scintillation and TEC Monitor receivers located in the Svalbard Islands, in Norway and in Antarctica have been analyzed. The aim is to describe the “scintillation climatology” of the high-latitude ionosphere over both the poles under quiet conditions of the near-Earth environment. For climatology we mean to assess the general recurrent features of the ionospheric irregularities dynamics and temporal evolution on long data series, trying to catch eventual correspondences with scintillation occurrence. In spite of the fact that the sites are not geomagnetically conjugate, long series of data recorded by the same kind of receivers provide a rare opportunity to draw a picture of the ionospheric features characterizing the scintillation conditions over high latitudes. The method adopted is the Ground Based Scintillation Climatology, which produces maps of scintillation occurrence and of total electron content relative variation to investigate ionospheric scintillations scenario in terms of geomagnetic and geographic coordinates, interplanetary magnetic field conditions and seasonal variability. By means of such a novel and original description of the ionospheric irregularities, our work provides insights to speculate on the cause-effect mechanisms producing scintillations, suggesting the roles of the high-latitude ionospheric trough, of the auroral boundaries and of the polar cap ionosphere in hosting those irregularities causing scintillations over both the hemispheres at high latitude. The method can constitute a first step toward the development of new algorithms to forecast the scintillations during space weather events.

Bipolar climatology of GPS ionospheric scintillation at solar minimum

[1] This paper presents statistical analysis of arctic auroral oval ionospheric scintillation events during the current solar maximum based on high-rate Global Positioning System data collected in Gakona, Alaska (62.39°N, 145.15°W) from August 2010 to March 2013. The objective is to gain a better understanding of the climatology and morphology of ionospheric scintillation in high-latitude regions. A scintillation event filter, multipath identification procedures, and other processes are applied to exclude nonscintillation related signal intensity and phase fluctuation and to extract scintillation events with S4 index above 0.12 and phase sigma above 6° from over 657 days of data. A total of over 5800 scintillation events were identified; most of them show phase fluctuations, only 10% of the phase fluctuations are accompanied by weak amplitude scintillation. Based on the occurrence time, signal direction of arrival, intensity, and duration of these scintillation events and the solar and geomagnetic activities associated with these events, diurnal, seasonal, spatial, and solar activity dependencies are derived and presented in the paper.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013RS005259

Characterization of high‐latitude ionospheric scintillation of GPS signals

Radio signal scintillation caused by electron density irregularities in the ionosphere affects the accuracy and integrity of Global Navigation Satellite Systems, especially in the equatorial and high-latitude regions during solar maxima. Scintillation in these two regions, nevertheless, is usually influenced by different factors and thus has different characteristics that cause different effects on GNSS signals. This paper compares the characteristics of high-latitude and equatorial scintillation using multifrequency GPS scintillation data collected at Gakona, Alaska, Jicamarca, Peru, and Ascension Island during the 24th solar maximum. Several statistical distributions are established based on the data to characterize the intensity, duration, and occurrence frequency of scintillation. Results show that scintillation in the equatorial region is generally more severe and longer lasting, while high-latitude scintillation is, in general, more moderate and usually dominated by phase fluctuations. Results also reveal the different impacts of solar activity, geomagnetic activity, and seasons on scintillation in different geographic locations.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015RS005719

Comparison of the effect of high-latitude and equatorial ionospheric scintillation on GPS signals during the maximum of solar cycle 24

Amplitude and phase scintillation measurements have been made at a high-latitude site over northern Europe during a 2-year period. Transmissions from the polar-orbiting multisatellite Navy Navigation Satellite System have been used to achieve both latitudinal and temporal coverage of the observations, with more than 12,000 satellite passes being monitored to yield in excess of 400,000 values of each of the S4 and σф indices for amplitude and phase scintillation respectively. Results are presented of scintillation occurrence for season, time of day and geomagnetic activity. A premidnight maximum and more scintillation activity in summer and autumn than in winter and early spring are apparent. The results demonstrate the importance of propagation geometry to high-latitude scintillation measurements, and estimates of the geometrical factors in both S4 and σϕ, computed for a model using different irregularity anisotropies, are discussed.

Amplitude and phase scintillation at high latitudes over northern Europe

Small scale irregularities associated with a high latitude electron density gradient: scintillation and EISCAT observations

Small scale ionospheric irregularities near regions of soft particle precipitation: scintillation and EISCAT observations

: Results are presented of studies of ionospheric scintillation job obtained by monitoring of transmissions from NNSS satellites at Kiruna, Northern Sweden during a two year period from September 1984 to September 1987. Attention is concentrated in this report on phase scintillation morphology. Also presented are results of model studies of the geometrical influences in amplitude and phase scintillations at a high-latitude site aimed at interpreting the observations and understanding the nature of the ionospheric irregularities responsible for the scintillations. Also discussed are results of two coordinated studies of ionospheric irregularities using scintillation observations and data from Hf and VHF backscatter radar systems respectively. Keywords: Radio-wave scintillations, Ionospheric irregularities, and High-latitude ionosphere.

N. S. Wheadon

Papers

Amplitude and phase scintillation at high latitudes over northern Europe

Small scale irregularities associated with a high latitude electron density gradient: scintillation and EISCAT observations

Small scale ionospheric irregularities near regions of soft particle precipitation: scintillation and EISCAT observations

Radio-Wave Scintillations and Ionospheric Irregularities at High Latitudes.